1. Technical Field
The present invention generally relates to low and medium sulfur, phosphorus, and sulfated ash (low and medium “SAPS”) lubricating oil compositions to enhance piston cleanliness in internal combustion engines.
2. Description of the Related Art
The viscosity grade of an engine oil is a key feature when selecting a lubricating oil. The lubricating oil is typically chosen according to both the climatic temperatures to which the engine is exposed, and the temperatures and shear conditions under which the engine operates. Thus, the oil must be of sufficiently low viscosity at ambient temperatures to provide adequate lubrication upon cold starting of the engine, and capable of maintaining sufficient viscosity to lubricate the engine when it is under a full operating load.
The Society of Automotive Engineers classification system, SAE J300, defines engine oil grade viscosity specifications. Single grades are designated as SAE 20, 30, 40, 50, and 60 grade, and are defined by a low shear rate kinematic viscosity range at 100° C. (ASTM D445), as well as a minimum high shear rate viscosity at 150° C. (such as ASTM D4683, CEC L-36-A-90, or ASTM D5481). Engine oils designated as SAE 0W through 25W have been classified according to their low temperature cranking viscosities (ASTM D5293), low temperature pumping viscosities (ASTM4684), and a minimum kinematic viscosity at 100° C.
Multigrade lubricating oils perform over wide temperature ranges. Typically, they are identified by two numbers such as, for example, 5W-30 or 10W-30. The first number in the multigrade designation is associated with a safe cranking temperature (e.g., −20° C.) viscosity requirement for that multigrade oil as measured by a cold cranking simulator (CCS) under high shear rates (ASTM D5293). In general, lubricants that have low CCS viscosities allow the engine to crank more easily at lower temperatures and thus improve engine startability at those ambient temperatures.
The second number in the multigrade designation is associated with a lubricant's viscosity under normal operating temperatures and is measured in terms of the kinematic viscosity (Kv) at 100° C. (ASTM D445). The high temperature viscosity requirement brackets minimum and maximum kinematic viscosity at 100° C. Viscosity at high temperatures is desirable to prevent engine wear that would result if the lubricant thinned out too much during engine operation. However the lubricant should not be too viscous because excessive viscosity may cause unnecessary viscous drag and work to pump the lubricant which in turn can increase fuel consumption. In general, the lower a lubricants' Kv 100° C., the better the scores that lubricant achieves in fuel economy tests.
Thus, in order to qualify for a given multigrade oil designation a particular multigrade oil must simultaneously meet both strict low and high temperature viscosity requirements that are set by SAE specifications such as SAE J300.
Merely blending base stocks of different viscosity characteristics may not enable the formulator to meet the low and high temperature viscosity requirements of some multigrade oils. The formulator's primary tool for achieving this goal is an additive conventionally referred to as a viscosity modifier or viscosity index (V.I.) improver. Usually, to reach the minimum high temperature viscosity required, it is necessary to add significant amounts of viscosity modifier. However, the use of an increased amount of viscosity modifier results in increased low temperature lubricant viscosity. The ever increasing need to formulate crankcase lubricants that deliver improved performance in fuel economy tests is driving the industry to engine lubricants in the lower viscosity grades, such as SAE 0W-20, 0W-30, 5W-20 and 5W-30.
Concurrent with the demand for lower viscosity, high fuel economy lubricants, there has been a continued effort to reduce the content of sulfated ash, phosphorus and sulfur in the crankcase lubricant due to both environmental concerns and to insure compatibility with pollution control devices used in combination with modern engines (e.g., three-way catalytic converters and particulate traps). A particularly effective class of antioxidant-antiwear additives available to lubricant formulators is metal salts of dialkyldithiophosphates, particularly zinc salts thereof, commonly referred to as ZDDP. While such additives provide excellent performance, ZDDP contributes each of sulfated ash, phosphorus and sulfur to lubricants.
Catalytic converters typically contain one or more oxidation catalysts, NOx storage catalysts, and/or NH3 reduction catalysts. The catalysts contained therein generally comprise a combination of catalytic metals such as platinum, and metal oxides. Catalytic converters are installed in the exhaust systems, for example, the exhaust pipes of automobiles, to convert the toxic gases to nontoxic gases. The use of catalytic converters is thought to be essential in bucking global warming trends and combating other environmental detriments. The catalysts, however, can be poisoned and rendered less effective, if not useless, as a result of exposure to certain elements or compounds, especially phosphorus compounds such as ZDDP.
Particulate traps are usually installed in the exhaust system, especially in diesel engines, to prevent the carbon black particles or very fine condensate particles or agglomerates thereof (i.e., “diesel soot”) from being released into the environment. Aside from polluting air, water, and other elements of the environment, diesel soot is a recognized carcinogen. These traps, however, can be blocked by metallic ash which is the degradation product of metal-containing, lubricating oil additives including common ash-producing detergent additives.
To insure a long service life for the after-treatment devices, it is desirable to identify lubricating oil additives that exert a minimum negative impact on such devices. To this end, OEMs often set various limits for maximum sulfur, phosphorus, and/or sulfated ash levels for “new service fill” and “first fill” lubricants. For example, when used in light-duty passenger-car internal combustion engines, the sulfur levels are typically required to be at or below 0.30 wt. %, the phosphorus levels at or below 0.08 wt. %, and the sulfated ash content at or below 0.8 wt. %. The maximum sulfur, phosphorus and/or sulfated ash levels may differ, however, when the lubricating compositions are used in heavy-duty internal combustion engines. For example, the maximum sulfated ash level may be as high as 1.6 wt. % in those heavy-duty engines. Such lubricating oil compositions are also referred to as “medium SAPS” (i.e., medium sulfated ash, phosphorus, and sulfur). When the maximum sulfated ash level is as high as 1.0 wt. %, the lubricating oil compositions are referred to as “low SAPS” lubricating oil compositions, e.g., for gasoline engines, and “LEDL” (i.e., low emission diesel lubricant) oil compositions for diesel engines.
Various tests have been established and standardized to measure the levels of SAPS in any particular lubricating oil compositions. For example, in Europe, a lubricant meeting the ACEA gasoline and diesel engine low SAPS specification must pass, inter alia, the “CEC L-78-T-99” test, which measures the cleanliness and extent of piston ring sticking after running a Volkswagen turbocharged direct injection automotive diesel engine for an extended time period, cycling alternatively between idle and full power. Similar specifications and testing standards of varied stringencies can also be found in other countries and regions, such as Japan, Canada, and the United States.
Meeting the low SAPS environmental standards however does not eliminate the need to provide adequate lubricant performance. Automobile spark ignition and diesel engines have valve train systems, including valves, cams, and rocker arms, all of which must be lubricated and protected from wear. Further, engine oils must provide sufficient detergency so as to insure engine cleanliness and suppress the production of deposits, which are products of non-combustibles and incomplete, combustibles of hydrocarbon fuels and deterioration of engine oils.
As discussed above, the need to preserve the integrity of catalytic converters has led to the use of less phosphate and phosphorus-containing additives. However, the use of detergents, which are typically metal sulfonate detergents, is often inevitable because of the sustained needs to neutralize the oxidation-derived acids and suspend polar oxidation residues in the lubricant. These detergents, however, contribute to the production of sulfated ash. The amount of ash permitted under most of the current environmental standards can be exceeded by far less metal sulfonate detergent than is necessary to achieve adequate detergency performance. Reducing the levels of detergent overbasing may reduce the level of ash produced, but it also reduces the acid neutralizing capacity of the lubricant composition, potentially leading to acid corrosion of the engine pistons and other parts.
Oil-soluble Mannich condensation products are useful in internal combustion engine lubricating oils. These products generally act as dispersants to disperse sludge, varnish, and lacquer, and prevent the formation of deposits. In general, conventional oil-soluble Mannich condensation products are formed from the reaction of polyisobutyl-substituted phenols with formaldehyde and an amine or a polyamine. For example, U.S. Pat. Nos. 7,964,543; 8,394,747; 8,455,681; 8,722,927 and 8,729,297 disclose that 0.01 wt. % to 10.0 wt. % of a Mannich condensation product formed by combining, under reaction conditions, a polyisobutyl-substituted hydroxyaromatic compound wherein the polyisobutyl group is derived from polyisobutene containing at least 50 weight percent methylvinylidene isomer and having a number average molecular weight in the range of about 400 to about 5000, an aldehyde, an amino acid or ester thereof, and an alkali metal base, can be used in an engine lubricating oil composition. Each of these patents further disclose in the examples that 1 wt. % of the Mannich condensation product was added to a fully formulated SAE grade 5W-30 baseline oil, SAE grade 5W-40 baseline oil and a SAE grade 10W-40 baseline oil.
Thus, there is a need to provide an improved low and medium SAPS lubricating oil composition which is a SAE 0W multi-grade lubricant that can overcome poor fuel economy performance.